1. Field of the Invention
The present invention generally relates to a process for forming battery cell containers and, more particularly, pertains to a process for forming cell containers having longitudinal ribs formed therein to improve the electrical and physical contact between the inner wall of the cell container and the electrochemical materials disposed therein.
The present inventive concept provides a novel single step process for forming a metal cell container having longitudinal, internally projecting ribs which provide increased contact area between cell container and the electrochemical material, normally a cathode, disposed therein.
2. Description of the Prior Art
Various fabrication procedures have been employed heretofore for the production of cans of the general type commonly used for beverages and food products. Some of these techniques have been used in the making of containers utilized in cylindrical alkaline batteries, yet none of the prior art methods of forming battery cans forms a cell having longitudinal ribs internally extending and integrally formed simultaneously with the formation of the can body.
One prior art method of producing a one-piece aluminum can body for beverages is to use progressive drawing dies to produce an aluminum body of somewhat less than the desired axial dimension and then to place the body on a mandrel for the purpose of ironing the cylindrical wall of the body by means of a hard metal or carbide ring to thin the metal and to elongate the cylindrical wall to the desired axial dimension. An improvement over this type of processing is disclosed in Fraze, U.S. Pat. No. 3,572,271, which discloses a process for fabricating can bodies having an integral bottom wall. Instead of simply ironing the can while on the mandrel, U.S. Pat. No. 3,572,271 employs a spinning operation which utilizes instead of ironing rings, a rolling means, such as a steel ball, which helically spins around the circumference of the metal while on the mandrel to not only thin the walls of the container but to also cold work the metal to actually heal defects within the metal such as cracks.
Another process for forming cans, and in particular, battery containers, includes taking a metal blank and forming it into a cup-like shape, placing the configuration onto a punch and forcing the metal through a series of ironing rings, each successive ring having an inner diameter smaller than the previous one. In this manner, a container can be produced having an integrally formed bottom wall, and a relatively thin side wall.
Yet another prior art method of producing a one-piece aluminum can body employs impact extrusion to produce an intermediate cup-shaped workpiece. It is not practical to extrude such a workpiece in a single impact stroke because it would be too severe on the dies involved and because slight defects in the metal and the presence of minute bodies of lubricant would result in too many rejects. Therefore, repeated extrusion is employed. The product of the repeated extrusion is placed on a mandrel and is finished to the desired final dimension by using a hard metal ring for a simple ironing operation.
The above-mentioned processes, however, do not teach any solution to the particular problem to which the present invention is directed.
To solve the problem of providing internal ribs, a well known process has previously been employed. Particularly, a two-step formation and drawing process has been employed to form the internally projecting ribs. Typically, after the can has been formed by any of the above-mentioned techniques, the ribs are then drawn onto the can in a secondary operation which can be, for example, by hydroforming or magnaforming.
The present inventive process, however is designed to circumvent the necessity of this or any other secondary operation, thereby inherently decreasing the cost of each item produced. None of the prior art of which Roper, U.S. Pat. No. 4,238,949, Yamaguchi, U.S. Pat. No. 3,608,350, and Connery, U.S. Pat. No. 1,534,299 are typical, even remotely suggests the simple and effective method of the present invention.
Roper, U.S. Pat. No. 4,238,949, discloses a method and apparatus for making metal outers and inners which are typically used in automobile suspension systems. This reference discloses a process for forming a metal annular member having precise tolerances and desired surface finishes. This reference utilizes novel extrusion techniques but does not disclose any process for making longitudinal ribs during the member formation process.
Yamaguchi, U.S. Pat. No. 3,608,350, discloses a method and apparatus for producing commutators for miniature electric machines such as dynamos, starters, and the like, normally for use in automobiles. This reference discloses placing a metal blank into a die having a number of grooves therein, the blank subsequently being pressed by means of extrusion by a punch provided with projecting teeth which correspond to the grooves of the die so as to provide the commutator shape desired. This reference, therefore, discloses a method for making externally projecting teeth on a metal commutator and does not relate to internally projecting ribs.
Connery, U.S. Pat. No. 1,534,299, discloses a corrugation forming die for metal plates having a punch which is fluted so as to construct the walls of the metal corrugation with flutes or other shapes. This reference discloses a punch, used to extrude a piece of metal with a compatible similarly shaped die. This reference is provided to give an overall view of the container art, yet it is not considered to be in a field at all analogous to the present invention.
Consequently, none of the known prior art is particularly directed to a single-step forming operation for providing battery cell containers having internally projecting ribs.